To decrease dependence of a color tone in a liquid crystal display device on an angle, a retardation film which satisfies a relation of 0.92≦R40/Re≦1.08, in which Re is a retardation value at an incident angle of 0 degrees, and R40 is a retardation value at an incident angle of 40 degrees, or a retardation film which satisfies a relation of nx>nz>ny, in which nx is a refractive index in a slow axis direction in a plane, ny is a refractive index in a direction at a right angle to the slow axis direction in the plane, and nz is a refractive index in a thickness direction, have been proposed.
For example, Patent Document 1 discloses that a first anisotropic film is obtained by uniaxially stretching a polycarbonate resin film, a second anisotropic film is obtained by uniaxially stretching a polystyrene resin film on the other hand, and then a retardation film which satisfies a relation of nx>nz>ny is obtained by overlapping the first anisotropic film and the second anisotropic film so that the directions of stretching of the films are at right angles to each other.
Patent Document 2 discloses that a first anisotropic film is obtained by uniaxially stretching a polycarbonate resin film, a second anisotropic film is obtained by uniaxially stretching a polystyrene resin film on the other hand, and then a retardation film which satisfies a relation of (Re−Re40)/Re≦0.07 is obtained by overlapping the first anisotropic film and the second anisotropic film so that the directions of stretching are at right angle to each other.
In these producing methods described in the patent document 1 or patent document 2, an accurate axis match is required when the films are stuck together.
Patent Document 3 discloses that a laminated body is formed by bonding a shrinkable film to one side or both sides of a resin film before the resin film is stretched, and stretching and heating of the laminated body so as to give a contractive force in a direction perpendicular to a stretching direction of the above-mentioned resin film results in obtaining a retardation film which satisfies a relation of 0<(nx−nz)/(nx−ny)<1.
In the producing method described in the patent document 3, the contractive force should be controlled accurately.
Patent Document 4 discloses that a rod is obtained by extrusion molding of a melted polycarbonate resin, a disc is obtained by slicing up the rod in round, a rectangular film is obtained by cutting the disc, and then a retardation film which satisfies a relation of 0.92≦Re40/Re≦1.08 is obtained by uniaxially stretching the rectangular film.
However, it is difficult to produce the retardation film having a large area by the producing method described in the Patent Document 4.